A conventional bearing for linear sliding motion of a type described above generally has a construction shown in FIG. 17. Specifically, it is formed of a track bed (or track member) (b) having rolling surfaces (b1) on which rolling members (a) such as balls roll in an axial direction; a slide bed (or slide member) (c) having load rolling surfaces (c1), which cooperate with the rolling surfaces (b1) to hold the rolling members (a) therebetween, and no-load rolling apertures (c2) corresponding to the load rolling surfaces (c1); and covers (d) for coupling and connecting the load rolling surfaces (c1) and the no-load rolling apertures (c2) to form endless paths for the rolling members (a). In this construction, the rolling member (a) rolls through load regions between the rolling surfaces b1 of the track member (b) and the load rolling surfaces (c1) of the slide member (c), whereby the slide bed (c) can linearly move along the track member (b) with a remarkably small frictional resistance.
A table for linear sliding motion, which supports a machine tool or a work for guiding them, generally has a construction shown in FIGS. 18 and 19, in which a plurality of track members (b) (two in the Figure) used for the bearings for the linear sliding motion are disposed on a fixing portion (e), and a plurality of sliding members (c) (two in the Figure) for carrying a table (f) are assembled to each track bed with a space between one another.
However, such bearings for the linear sliding motion have following disadvantages with respect to the motion of the slide members due to its construction.
First, minute vibration called as "waving" is generated in the slide members. In the bearing for the linear sliding motion including the rolling members which circulate and perform an endless movement for the slide member, the rolling members are generally in preloaded conditions when they roll through a load region in order to increase rigidity of the slide member with respect to the track member and prevent rattling thereof. Therefore, when the rolling members are forcedly entered into the load region or released from the load region, the slide member minutely deviates in vertical or lateral directions, which causes the minute vibration, i.e., waving during the movement of the slide member.
A second disadvantage relates to a linearity of a motion of the slide member. It is ideal for the slide bed to move linearly with respect to the fixing portion on which the track member is disposed. However, the motion thereof is inevitably affected by a mounting accuracy of the track member to the fixing portion and a machining accuracy of the rolling surfaces, and thus it is very difficult in practice to obtain a high linearity of the movement. If it is attempted to obtain the desired linearity of the movement by increasing the mounting accuracy of the track member and the machining accuracy of the rolling surfaces, disadvantages such as high costs and low productive efficiency will be caused. Therefore, in view of the above, the linearity of the movement can be improved only to a restricted extent.
The disadvantages of the motion of the slide member described above form an important factor which cannot be overlooked in machine tools or the like which are guided by the bearings for the linear motion during machining operations, because the waving of the slide members or the insufficient linearity of the movement causes deviation of the tools of the machine tools, and thus directly affects the machining accuracy of the products.
However, in the recent industrial application, demands for higher accuracies in various products, and thus demands for higher machining accuracies have been increased in the machines and apparatuses such as machine tools for machining these products.
Accordingly, the bearings for the linear sliding motion for performing linear guiding in various machines and apparatuses have been required to prevent the waving during movement or travelling of the slide beds and to improve the linearity of the movement.
On the other hand, with respect to the tables for the linear sliding motion, reduction of costs has been attempted by minimizing thicknesses of tables which are mounted on the slide members in the recent years. However, this adversely affects the rigidity, and specifically, this may cause deflection or the like in the tables which may reduce the machining accuracies of machine tools mounted thereon.
In view of the above demands and problems, it is an object of the invention to provide a bearing for linear sliding motion, which can minimize the waving of the slide member and improve the linearity of the movement.
Another object of the invention is to provide a table for linear sliding motion which allows machining with a high accuracy by a machine or apparatus such as a machine tool mounted thereon.